1. Field of the Invention
The present invention relates to a diffraction grating device in which a diffraction grating is formed through refractive index modulation along the longitudinal direction of an optical waveguide, and a method and apparatus for manufacturing such a diffraction grating device.
2. Related Background Art
A diffraction grating device is a device in which a diffraction grating is formed through refractive index modulation along the longitudinal direction of an optical waveguide (e.g. an optical fiber). Broadly classifying such diffraction grating devices, Bragg-type ones for which the period of the refractive index modulation is relatively short and which use Bragg reflection, and long-period-type ones for which the period of the refractive index modulation is relatively long and which use phase matching between propagation modes are known. A Bragg-type diffraction grating device is capable of selectively reflecting light of a specific wavelength that satisfies the Bragg condition out of light propagating along the optical waveguide, and is used, for example, as a wavelength filter in an optical communication system. A long-period-type diffraction grating device is capable of selectively giving loss to light of a specific wavelength that satisfies a phase matching condition out of light propagating along the optical waveguide, and is used, for example, as a loss filter in an optical communication system.
Such diffraction grating devices are manufactured as follows. First, an optical waveguide for which the optical waveguiding region is photosensitive is prepared. For example, an optical fiber having a core region comprising silica glass to which GeO2 has been added is prepared. Silica glass to which GeO2 has been added is photosensitive, with the refractive index rising upon being irradiated with ultraviolet light. Refractive-index-change-inducing light of a wavelength that induces such a change in refractive index is thus irradiated onto the optical waveguide via a phase grating mask or an intensity modulating mask while scanning along the longitudinal direction. Through this irradiation, refractive-index-change-inducing light whose intensity is spatially modulated along the longitudinal direction of the optical waveguide is irradiated, and hence refractive index modulation is formed along the longitudinal direction of the optical waveguiding region of the optical waveguide.
As a result of studying the prior art described above, the present inventors discovered the following problems. A laser light source is used as the light source that outputs the refractive-index-change-inducing light. In general the light outputted from a laser light source has a Gaussian intensity distribution in the radial direction, and the beam diameter is small. Consequently, when such laser light is irradiated as the refractive-index-change-inducing light onto the optical waveguide, in the case that the accuracy of the direction of emission of the refractive-index-change-inducing light from the light source is poor, or the case that the accuracy of alignment of optical elements on the optical path from the light source to the optical waveguide is poor, the refractive-index-change-inducing light may not be irradiated with uniform intensity in the radial direction onto the part of the optical waveguide that is photosensitive, or the refractive-index-change-inducing light may not be irradiated with the desired intensity distribution when scanning along the longitudinal direction.
If the refractive-index-change-inducing light is not irradiated with uniform intensity in the radial direction, or if the refractive-index-change-inducing light is not irradiated with the desired intensity distribution when scanning along the longitudinal direction, then the diffraction grating device obtained will not have the desired optical characteristics. In particular, with a diffraction grating device in which not only the core region but also part of the cladding region is made to be photosensitive and refractive index modulation is formed over both the core region and the cladding region, or a diffraction grating device in which the grating plane of refractive index modulation formed over both the core region and the cladding region is inclined, or a diffraction grating device in which the amplitude distribution of the refractive index modulation along the longitudinal direction is made to have a prescribed functional form, the intended desired optical characteristics will not be obtained.
The present invention was devised to resolve the problems described above; it is an object of the present invention to provide a method and apparatus that enable a diffraction grating device having desired optical characteristics to be manufactured easily.
The present invention provides a diffraction grating device manufacturing method, in which refractive-index-change-inducing light of a wavelength that induces a change in refractive index is irradiated onto an optical waveguide, thus forming a diffraction grating through refractive index modulation along the longitudinal direction of the optical waveguide, wherein the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide is swung in a direction perpendicular to the longitudinal direction of the optical waveguide.
The present invention also provides a diffraction grating device manufacturing apparatus that irradiates refractive-index-change-inducing light of a wavelength that induces a change in refractive index onto an optical waveguide, thus forming a diffraction grating through refractive index modulation along the longitudinal direction of the optical waveguide, the diffraction grating device manufacturing apparatus comprising (1) a light source that outputs the refractive-index-change-inducing light, (2) irradiation means for irradiating the refractive-index-change-inducing light that has been outputted from the light source onto the optical waveguide, and (3) swinging means for swinging the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide by the irradiation means in a direction perpendicular to the longitudinal direction of the optical waveguide.
Moreover, the present invention also provides a diffraction grating device manufactured using the diffraction grating device manufacturing method described above.
In the present invention, refractive-index-change-inducing light of a wavelength that induces a change in refractive index is irradiated onto an optical waveguide, and the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide is swung in a direction perpendicular to the longitudinal direction of the optical waveguide. A diffraction grating device manufactured in this way has a diffraction grating formed through refractive index modulation along the longitudinal direction of the optical waveguide; the refractive-index-change-inducing light is irradiated with a desired intensity distribution onto a photosensitive region of the optical waveguide in which the diffraction grating is to be formed, and hence the diffraction grating device has desired optical characteristics.
It is preferable for the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide to be swung with an amplitude of at least 30 xcexcm in the direction perpendicular to the longitudinal direction of the optical waveguide. Moreover, it is preferable for the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide to be scanned at a scanning speed vS in the longitudinal direction of the optical waveguide, and the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide to be swung at a swing speed vB, which is faster than the scanning speed vS, in the direction perpendicular to the longitudinal direction of the optical waveguide. As a result, the intensity distribution of the refractive-index-change-inducing light irradiated onto the photosensitive region of the optical waveguide in which the diffraction grating is to be formed becomes yet closer to the desired distribution.
The present invention can be understood more fully through the following detailed description and the attached drawings; however, the following is merely given for illustrative purposes, and should not be regarded as limiting the present invention.